From: Andrew Morton <akpm@linux-foundation.org>
To: Minchan Kim <minchan@kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>,
Suren Baghdasaryan <surenb@google.com>,
Michal Hocko <mhocko@suse.com>, John Dias <joaodias@google.com>,
Tim Murray <timmurray@google.com>,
Matthew Wilcox <willy@infradead.org>,
Vladimir Davydov <vdavydov.dev@gmail.com>,
Martin Liu <liumartin@google.com>,
Johannes Weiner <hannes@cmpxchg.org>
Subject: Re: [PATCH v4] mm: don't be stuck to rmap lock on reclaim path
Date: Wed, 11 May 2022 15:33:49 -0700 [thread overview]
Message-ID: <20220511153349.045ab3865f25920dce11ca16@linux-foundation.org> (raw)
In-Reply-To: <20220510215423.164547-1-minchan@kernel.org>
On Tue, 10 May 2022 14:54:23 -0700 Minchan Kim <minchan@kernel.org> wrote:
> The rmap locks(i_mmap_rwsem and anon_vma->root->rwsem) could be
> contended under memory pressure if processes keep working on
> their vmas(e.g., fork, mmap, munmap). It makes reclaim path
> stuck. In our real workload traces, we see kswapd is waiting the
> lock for 300ms+(worst case, a sec) and it makes other processes
> entering direct reclaim, which were also stuck on the lock.
>
> This patch makes lru aging path try_lock mode like shink_page_list
> so the reclaim context will keep working with next lru pages
> without being stuck. if it found the rmap lock contended, it rotates
> the page back to head of lru in both active/inactive lrus to make
> them consistent behavior, which is basic starting point rather than
> adding more heristic.
>
> Since this patch introduces a new "contended" field as out-param
> along with try_lock in-param in rmap_walk_control, it's not
> immutable any longer if the try_lock is set so remove const
> keywords on rmap related functions. Since rmap walking is already
> expensive operation, I doubt the const would help sizable benefit(
> And we didn't have it until 5.17).
>
> In a heavy app workload in Android, trace shows following statistics.
> It almost removes rmap lock contention from reclaim path.
What might be the worst-case failure modes using this approach?
Could we burn much CPU time pointlessly churning though the LRU? Could
it mess up aging decisions enough to be performance-affecting in any
workload?
Something else?
next prev parent reply other threads:[~2022-05-11 22:33 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-10 21:54 [PATCH v4] mm: don't be stuck to rmap lock on reclaim path Minchan Kim
2022-05-10 22:26 ` Johannes Weiner
2022-05-11 22:33 ` Andrew Morton [this message]
2022-05-11 22:57 ` Minchan Kim
2022-05-12 2:05 ` Andrew Morton
2022-05-12 19:55 ` Minchan Kim
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